I'm at work. Currently, we're having some fierce networking problems and every website I try to open throws an error similar to Firefox can't find the server at www.google.com.. However, I can still browse StackOverflow and I am posting this, which proves that I'm not reading from cache.

For this specific issue it sounds like @Franci Penov and @iftrue are right - you're having DNS issues.

On a more general level you should make sure you have some sort of connectivity in case your primary network goes down. This can be a separate connection (DSL + cable or dialup), a cell phone with a data plan and tethering, or the local coffee shop.

dig is your friend here for analysing DNS issues. If you're a Windows man like me, you can get dig for Windows from Nicholas Fong's site. (site also has basic user guide on it) - if you can't resolve it, the server's IP is 64.59.134.11 for your hosts file!

(or similar) in the results, then your DNS server's poorly. If you get a list of results in the ANSWER section including www.google.com, www.l.google.com and www-tmmdi.l.google.com (for example) then your DNS resolver is working and your own PC is not.